This invention relates to actuator systems of the type having a motor and a feedback device when the feedback device is connected to an output shaft of the motor.
Actuator systems are used for driving a driven member in a wide variety of applications. By way of example, actuators are used in automotive climate controls to adjust the various air duct doors. Further, these doors are used to blend heated, cooled or ambient air according to a selected temperature setting and to direct the air to the selected vents.
Actuators are generally part of a control system that accepts instructions from a user and directs the movement of the actuators according to those instructions. The control system often needs to have information regarding the current position of the output shaft of the motor. The position of the output shaft is provided by the feedback device. The feedback device may be a potentiometer having a wiper that is mechanically coupled and driven by the output shaft of the motor.
As shown in FIG. 1A, earlier prior art solutions utilized a five-wire actuator system. Typical applications have a processor (not shown), two motor drivers (not shown) and an analog-to-digital converter (not shown). A motor 10 is connected to the two drivers through a first port 12 and a fifth port 20. It will be understood that the motor has an output shaft connected to the device to be driven. The output shaft also carries a wiper 22 of a potentiometer 24. Wiper 22 is connected to the analog-to-digital converter through a third port 16. A power supply (not shown) is connected to one side of potentiometer 24 through a second port 14 while the other side is grounded through a fourth port 18. A motor power supply (not shown) is connected to the two motor drivers.
In this system, five wires are needed to connect motor 10 and potentiometer 24 to first port 12, second port 14, third port 16, fourth port 18, and fifth port 20. The output voltage of third port 16 is proportional to a position of the output shaft. Note that potentiometer 24 requires a potentiometer power supply (not shown), separate from the power supply. The potentiometer power supply and its associated wiring add cost and complexity to the system. The three-wire and four-wire systems of the present invention have been developed to minimize these costs.
While the device of U.S. Pat. No. 5,389,864 issued to Tryan et al, achieves its intended purpose of eliminating the potentiometer power supply, significant disadvantages still exist. As shown in FIG. 1B, the actuator system consists of a first port 26, a second port 28, a third port 30, a motor 32, and a potentiometer 34. First port 26 and third port 30 connect a power supply (not shown) to motor 32 and potentiometer 34. Second port 28 is connected to an analog-to-digital converter (not shown) with the purpose of providing a voltage indicative of the position of the output shaft, The disadvantages of this system are that second port 28 will only provide voltage indicative of the position of the output shaft when motor 32 is powered by the power supply. To solve this problem, a short pulse must be produced by the power supply long enough to produce a voltage indicative of position of the output shaft, but short enough not to move motor 32, which may cause an error in the voltage indicative of the position of the output shaft. Last, complex software must be developed to differentiate which direction motor 32 is moving to correctly interpret the voltage indicative of the position of the output shaft.
Furthermore, in the device disclosed in U.S. Pat. No. 5,744,925 issued to Madsen, achieves its intended purpose of eliminating the potentiometer power supply, however significant disadvantages still exist. As shown in FIG. 1C, the actuator system consists of a first port 36, a second port 38, a motor 40, a potentiometer 42, a resistor 44, a first zener diode 46, and a second zener diode 48. Potentiometer 42 and resistor 44 are connected in series across first port 36 and second port 38 and will produce a voltage indicative of the position of the output shaft when a current passes through potentiometer 42 and resistor 44. Motor 40, first zener diode 46 and second zener diode 48 are connected in series across first port 36 and second port 38. More specifically, first zener diode 46 and second zener diode 48 are connected in a back-to-back configuration. The back-to-back configuration will only allow a flow of current through motor 40 when the voltage across first port 36 and second port 38 reaches a threshold voltage. A voltage reading can be taken across potentiometer 42 and resistor 44 without moving the motor when the voltage across first port 36 and second port 38 is below the threshold voltage. The disadvantages of this system are that a voltage reading across potentiometer 42 and resistor 44 can only be taken when the voltage across first port 36 and second port 38 are below the threshold voltage. Next, motor 40 will need to be a larger motor due to a greater voltage required to exceed the threshold voltage. Last, first zener diode 46 and second zener diode 48 are components that are not commonly found on an actuator and would increase manufacturing costs.
Therefore, there is a need for a new and improved device that allows a reading of the position of the output shaft without requiring the motor to move, does not require a larger, more costly motor, and does not require any components not commonly found on an actuator. At the same time, the device should be less costly than devices currently used.
In an aspect of the present invention, an actuator and controller is provided. The actuator has a motor and a potentiometer. The motor has an output shaft, a first drive contact and a second drive contact. The potentiometer has a first potentiometer contact, a second potentiometer contact and a potentiometer feedback contact. The first potentiometer contact is connected to one of the first drive contact, the second drive contact and a grounded contact, the second potentiometer contact is connected to the potentiometer feedback contact, thereby producing a feedback signal indicative of a position of the output shaft. The controller has a feedback port, a first motor control port, and a second motor control port. The feedback port is connected to the second potentiometer contact and the potentiometer feedback contact. The first motor control port is connected to the first drive contact and the second motor control port is connected to the second drive contact.
In accordance with another aspect of the present invention, the feedback signal is indicative of an electrical impedance.
In accordance with another aspect of the present invention, the first potentiometer contact is connected to the first drive contact.
In accordance with another aspect of the present invention, the first potentiometer contact is connected to the second drive contact.
In accordance with another aspect of the present invention, the first potentiometer contact is connected to the grounded contact.
In accordance with another aspect of the present invention, the controller further comprises a pull-up resistor connected to the feedback port.
In accordance with another aspect of the present invention, the controller further comprises a pull-down resistor connected to the first motor control port.
In accordance with another aspect of the present invention, the controller further comprises an analog-to-digital converter. The analog-to-digital converter has an analog input and a digital output. The analog input is connected to the feedback port. The digital output is connected to the processor.
In accordance with another aspect of the present invention, the digital-to-analog converter is integrated within the processor.
In accordance with another aspect of the present invention, the controller further comprises a first motor driver and a second motor driver. The first motor driver has a first motor driver output and a first motor driver input and the second motor driver has a second motor driver output and a second motor driver input. The first motor driver output is connected to the first motor control port and a second motor driver output is connected to the second motor control port. The first motor driver input is connected to the processor and the second motor driver input is connected to the processor.
In accordance with another aspect of the present invention, the controller further comprises a differential amplifier. The differential amplifier has a first differential input, a second differential input and a differential output. The first differential input is connected to the feedback port. The second differential input is connected to the second motor control port.
In accordance with another aspect of the present invention, the controller further comprises an analog-to-digital converter. The analog-to-digital converter has an analog input and a digital output. The analog input is connected to the differential output. The digital input is connected to the processor
In accordance with another aspect of the present invention, the digital-to-analog converter is integrated within the processor.
These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying drawings.